In conventional control devices for controlling multicylinder internal combustion engines, a cylinder equalization control is provided for adjusting and/or equalizing cylinder-specific torque contributions to the overall torque of the internal combustion engine. The internal combustion may be a gasoline or diesel engine, for example. There is a special need for a cylinder-equalization function in direct-injection gasoline engines. In such engines, increased irregular operation can occur due to a low compatibility to tolerances of the combustion process in stratified operation and/or due to the tolerances of the high-pressure injectors used or in the distribution of the fuel to the individual cylinders. Age-related changes in the flow characteristic of the high-pressure injectors can also play a role. A cylinder equalization control can effect an improvement in running smoothness.
Within the framework of cylinder equalization, the active torque contribution (actual torque) of a particular cylinder is detected in relation to its preceding ignition, i.e., not as an absolute torque determination, based on an analysis of the time characteristic of the crankshaft or camshaft rotation. A torque correction can be effected, with the goal of equalizing cylinder-specific torque contributions, by intervening in at least one combustion-determining parameter, such as the injected fuel quantity, the ignition point timing in the case of a gasoline engine, in the exhaust-gas recirculation rate, or in the injection position. The term “injection position” refers here to the angular position of an injection pulse with respect to a reference point, for example to the top dead center of the piston of a cylinder in its power stroke.
In practice, cylinder-equalization controls, in which so-called segment periods are recorded to analyze the time characteristic of the moment of rotation of the crankshaft or camshaft, have proven to be particularly useful. Segment periods are the times it takes for the crankshaft or camshaft to cover a predefined angular range assigned to a particular cylinder. The more smoothly the engine is running, the more negligible the differences are between the segment periods of the individual cylinders. A measure of the engine's irregular operation can be derived from the mentioned segment periods. Conventional methods provide for an individual control to be assigned to each cylinder of the internal combustion engine and for the individual control to receive a cylinder-specific, irregular-operation actual value as an input signal. On the basis of the irregular-operation actual values, a control setpoint value is determined. For example, the irregular-operation values of a plurality of cylinders can be averaged to produce a control setpoint value. On the output side, the controls influence the cylinder-specific injection times and the cylinder-specific torque contributions such that the cylinder-specific actual values approach the setpoint value. Cylinder-equalization controls are described, for example, in European Patent No. 140 065 and in German Patent Application No. 198 28 279, the latter being incorporated for reference herein.